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Old 04-30-2008, 04:21 PM   #1 (permalink)
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4.2 to 4.0 swap

I am possibly getting a few more jeeps through a trade. My plans are basically do a quick once over, clean em up, fix whats wrong and sell them for a profit.

One of them is a 1988 YJ with the 4.2, body is decent, new paint, but it has a motor knock.

I have a running 4.0, but I dont have the computer and all that garbage, as well as a gas tank with a fuel injection pump, and I dont want to redo the fuel lines to injection lines. And for a jeep that Im not going to be driving, I dont want to run around finding it, because its going to be in the way the whole time I have it, and it needs to go as fast as possible.

Is it possible to swap the 4.0 in and run it with the 4.2 intake and carb, or even to swap the 4.2 head onto the 4.0 and just run the bottom end?

Or anyone have a simple solution? If theres nothing I guess Im going to have to search for a cheap 4.2 on craigslist
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Old 05-01-2008, 03:12 PM   #2 (permalink)
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Nobody?
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Old 05-01-2008, 03:46 PM   #3 (permalink)
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You can run the 4.0 head on the 4.2 and vise versa and as far as i know the intake matches up just don't run the 4.2 head on the 4.0 because you will do it an injustice. The 4.0 head flows better.
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Old 05-01-2008, 09:08 PM   #4 (permalink)
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So I will be able to run my 4.0 off of a carburetor?

If I just bolt the 4.2 intake with the carb onto the 4.0 head it will run fine? Thats the ideal scenario, makes the least amount of work for me.
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Old 05-01-2008, 11:01 PM   #5 (permalink)
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from what i understand if you have a running 4.0, you can swap it in with minmal work, as long as you have some sort of way to mount the carb (an intake manifold off of a carbed 4.2 will fit on a 4.0 head).

your two options are...

replace the 4.2 with the 4.0 and use the 4.2 carburetor intake. (the intake will bolt up to the head but you would have to use the exhaust manifold from the 4.0 because the 4.2 will not fit.) there are a bunch of write ups on swaps just gotta use the search.

orrrr....

pull the pan off the 4.2, and retorque the bolts on your mains, rods, and readjust your valves and leave the motor in there. if you do that you might as well replace your main bearings and rod bearings. once your done reinstall the motor and sell it to someone. the 4.2 is a good motor, its just the carb that ruins it.

everyone likes the 4.0 cause its higher output but if your just wheelin and dealin why waste the time and money to swap the 4.0 in when you can rebuild the 4.2 bottom end for the same if not less.

I think if you were gonna keep it, it would be worth adding the 4.0, but since your trying to get rid of it, i would just leave the knocking engine and sell it to someone who has the funds/interest in building or replacing the motor. you can still get good money for an 88 wrangler even if it has a rod knock. anyone with automotive experience can fix a knock. its really easy to pinpoint if your good, and the motor is running. =)

and btw that 4.0 is worth more on an engine stand then in a wrangler. someone somewhere is wanting to do this swap. why not just sell the wrangler, and then sell the 4.0?
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Old 05-02-2008, 05:25 AM   #6 (permalink)
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Well, Ive been trying to sell the motor for a while (Im in Vermont, theres really not many people lol) and it hasnt gone so I figured I might as well just get everything out of my hair at the same time...and keep the 4.2 to pull parts off for a future stroker
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Old 05-02-2008, 07:36 AM   #7 (permalink)
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You will also need to deal with ignition for the 4.0. You can use the 4.2 dizzy and ignition from it to go along with a carb conversion.
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Old 05-03-2008, 03:18 AM   #8 (permalink)
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Originally Posted by drewguere View Post
Well, Ive been trying to sell the motor for a while (Im in Vermont, theres really not many people lol) and it hasnt gone so I figured I might as well just get everything out of my hair at the same time...and keep the 4.2 to pull parts off for a future stroker
well in that case,

if your gonna do the swap, invest in the tfi upgrade (runs soo much nicer), use your 4.2 dizzy, swap in the 4.0 and stick the carb parts on it. you'll have a blast driving it, and you wont wanna sell it. lol

everything should work for you. if you were installing an FI 4.0 then you would need to do some work but since your just putting a carb on it, all you need is to put the long block in and bolt everything up to it. pretty simple...should only take a day. just dont forget to use the 4.0 header since the 4.2 wont work.

good luck
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Old 05-03-2008, 07:05 PM   #9 (permalink)
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i am also thinking of doing this swap. i know that if i swap in the 4.0 with my trans(tf999), i would need a crank position sensor. will i still need the cps if i swap all the carb stuff over to the 4.0?
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Old 05-04-2008, 12:26 AM   #10 (permalink)
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i am also thinking of doing this swap. i know that if i swap in the 4.0 with my trans(tf999), i would need a crank position sensor. will i still need the cps if i swap all the carb stuff over to the 4.0?
I would think a crank position sensor would be for the EFI ignition. you will need to keep it if you were using the efi. but since you are using a carburetor you can eliminate this by using the distributor and ignition module out of a cj/yj w/o efi.

randillo, if you have a cj or yj that is carbureted, then your ignition should work. and you wouldnt need a CPS
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Old 05-04-2008, 09:35 AM   #11 (permalink)
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well in that case,

if your gonna do the swap, invest in the tfi upgrade (runs soo much nicer), use your 4.2 dizzy, swap in the 4.0 and stick the carb parts on it. you'll have a blast driving it, and you wont wanna sell it. lol

everything should work for you. if you were installing an FI 4.0 then you would need to do some work but since your just putting a carb on it, all you need is to put the long block in and bolt everything up to it. pretty simple...should only take a day. just dont forget to use the 4.0 header since the 4.2 wont work.

good luck
What is the tfi upgrade? Ill look around and see if I can find any info on it

OK I found stuff thru search, so its just an ignition upgrade? What exactly is in the kit and where would I buy one?
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Last edited by drewguere; 05-04-2008 at 09:40 AM.
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Old 05-04-2008, 06:31 PM   #12 (permalink)
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It is basically just tune-up parts using mid 80s ford 300cid parts. You need the cap adapter, rotor, cap. Use the sparkplug wires from the 4.0. You can also combine this with the e-core coil. You'll need an ignition module. You can use the module from the 4.2 wired per the "nutter" instructions or use a GM 4 pin module.
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Old 05-05-2008, 12:40 AM   #13 (permalink)
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yeah its a ignition upgrade.

basically, the jeep distributor is a ford distributor with a different cap and rotor. the base part of the diz is kept but the top cap, rotor and wires are all trashed in favor of newer more easily replaceble parts.

the jeeps OEM setup is a low energy ignition, the TFI is a high energy ignition. the upgrade uses a base adapter, cap, rotor and wires for a 81 f-150 300ci I6. all these parts mount on the distrubutor without modifications.

this performs quite better then a stock set up, and you will notice it.

the "TFI" part of the upgrade, actually refers to the high energy coil designed by ford. it is said to be more powerful then the HEI ignition from chevy, and performs more noticably then any other upgrade. I have this on my jeep, the difference it made is phenominal. all i did was mount the TFI coil and put the wires to the old coil onto the new one. hardest part is mounting the coil.

you can get the coil at any local autoparts store. its for a 1984 F150 with the 5.0 v8.

all these parts make the ignition work better, and are easily available at any autostore. google "jeep tfi upgrade" and you will find more then you need to know about this setup.
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